This invention relates generally to swash plates and, more particularly, relates to a swash plate assembly for use in a hydrostatic transmission.
Currently known hydrostatic transmissions comprise a hydraulic pump unit and a hydraulic motor unit. The hydraulic pump unit is hydraulically connected to the hydraulic motor unit through hydraulic porting, which may be formed in the housing, a center section, or the like, to form what is referred to as a hydraulic circuit. The hydraulic pump unit comprises a pump cylinder block having a plurality of piston receiving chambers formed therein in each of which is disposed a movable pump piston. Similarly, the hydraulic motor unit comprises a motor cylinder block having a plurality of piston receiving chambers formed therein in each of which is disposed a movable motor piston. An example of a hydrostatic transmission utilizing a center section may be seen in U.S. Pat. No. 5,330,394 to Hauser et al. entitled "Rider Transaxle having Improved Casing Design" which is incorporated herein by reference in its entirety.
An input shaft, which is driven by the engine of a vehicle, is drivingly connected to the hydraulic pump unit such that the rotation of the input shaft rotates the pump cylinder block therewith. The rotation of the pump cylinder block causes the pump pistons to travel up and down as they travel against a movable, metallic swash plate. As will be understood by those skilled in the art, the swash plate may be moved to a variety of positions to vary the stroke of the pump pistons. In particular, as the stroke of the pump pistons is varied, the volume of the hydraulic fluid pumped into the hydraulic porting will vary. Since the speed of the hydraulic motor unit is dependent upon the amount of hydraulic fluid pumped thereinto by the hydraulic pump unit, the positioning of the swash plate is seen to control the speed of the hydraulic motor unit. More specifically, each of the motor pistons is driven by the pumped hydraulic fluid against a fixed, angularly orientated motor thrust bearing such that the action of the motor pistons thereagainst forces the motor cylinder block to rotate.
While the currently utilized metallic swash plate works well for its intended purpose, it is seen to suffer from a number of drawbacks. In particular, prior art metallic swash plates have been seen to be relatively costly to manufacture owing to, among other things, the costs associated with forming the part from powdered metal or machining the part after it is formed from cast iron or aluminum. It is also seen that machining such parts may lead to stress induced fractures of the components during the operation of the transmission. In addition, owing to the relatively non-resilient characteristic of such metallic swash plates, the relative tolerances with which the part must be manufactured further function to increase the cost of their production. Furthermore, the use of metallic material in the construction of such swash plates functions to undesirably increase the overall weight of the hydrostatic transmission. As a result of these drawbacks, it is seen that a need exists in the art for an improved swash plate which need not be constructed from a metallic material.
As a result of this existing need, it is an object of the present invention to provide an improved swash plate for use in a transmission. It is a further object of the present invention to provide a swash plate for use in a transmission which is relatively less costly to manufacture. It is yet a further object of the present invention to provide a swash plate for use in a transmission which is formed as a net shape part thereby eliminating the need for machining. It is still a further object of the present invention to provide a swash plate for use in a transmission which is generally resilient thereby requiring relatively less exacting manufacturing tolerances. It is yet another object of the present invention to provide a swash plate for use in a transmission which functions to reduce the overall weight of the transmission. It is still another object of the present invention to provide a swash plate which functions to reduce the overall noise associated with the operation of the transmission.